CDA and neoplasm: Capecitabine (N4-pentyloxycarbonyl-5′-deoxy-5-fluorocytidine, XelodaTM, Ro 09-1978, etc.)is an oral fluoropyrimidine carbamate [44], which is selectively converted to 5-FU in tumors through a cascade of three enzymes: (1) carboxylesterase, which is almost exclusively located in the liver and hepatoma, but not in other tumors and normal tissues; (2) cytidine deaminase, which is located in the liver and various types of solid tumors, and 3) dThdPase, which is more concentrated in various types of tumor tissues than in normal tissues (Figure 4).